A stimuli-responsive polymer of which volume or condition changes (it swells or shrinks) responding to a stimulus such as external heat, light, electric current, electric field and pH and which may be applicable to functional materials in various fields is generally known. For example, it has been suggested to be applied to drug carriers or anti-adhesive materials, medical materials for a drug delivery system, cosmetics, polymer actuator for driving moving parts of robots, chemical valve, material separator and optical elements. Particularly, the medical materials are regarded as the promising use of such materials.
Neighboring organs or organizations are adhered to each other when a wound such as inflammation, injury, excortication and operative wound heals. For example, an adhesion is caused after various surgeries accompanied with extirpation of diseased parts and restoration of damaged parts. A sheet type anti-adhesive material such as “SEPRAFILM” (made by Genzyme Biosurgery) and “INTERSEED” (made by Johnson & Johnson Company) is known as an adhesion barrier which works to prevent such an adhesion while a wound is healed in the body.
However, it is difficult for such an anti-adhesive material to be used for organs having a three-dimensional shape such as a cylinder shape or to medical equipment having a complex shape and are installed in the body. In addition, the above-described “SEPRAFILM” or the like may have poor handling ability when wet. Besides, it is too difficult for such a sheet type anti-adhesive material to be used in a recently increasing surgical operation using an endoscope or a laparoscope.
To improve the application convenience, a stimuli-responsive material supplied in a liquid state (or solid state) and produces an effect such as protection, separation, reinforcing and cushioning, in a solid state (or liquid state) brought about by a stimulus such as temperature change are known. JP 2003-252936-A discloses an application study of wound dressing material, surgical anti-adhesive material and adhesive with a material made of temperature-responsive polymer supplied as a liquid being fluid at room temperature into the body where it is solidified at body temperature and exhibits a barrier property after contacting the diseased parts in the operation using the endoscope or laparoscope.
A temperature-responsive polymer is one of such an attractive stimuli-responsive polymer. The temperature-responsive polymer generally includes two types of which a hydrated polymer is dehydrated to change the volume, formation or characteristics above the Lower Critical Solution Temperature (may be abbreviated as LCST) and of which a polymer is hydrated to change the volume, formation or characteristics below the Upper Critical Solution Temperature (may be abbreviated as UCST). The latter type of temperature-responsive polymer having the UCST may be a copolymer of N-acetyl acrylamide and acrylamide disclosed in JP 2000-86729-A. The former type of temperature-responsive polymer having the LCST may be a homopolymer or copolymer of N-isopropyl acrylamide (NIPAM) disclosed in JP 11-228850-A or may be a poloxamer. Particularly, a poly(N-isopropyl acrylamide) (PNIPAM)-based polymer compound is disclosed in JP 2004-307523-A. Such a compound changes volume as swelling-shrinking to form a solid gel around 32° C. close to body temperature and therefore it is expected to be applied to a medical material or the like.
Although such a stimuli-responsive polymer has an application convenience, it generally has too low an elasticity and strength to satisfy mechanical characteristics required for the use in a solid (gel) state. For example, it may have insufficient barrier characteristics for anti-adhesive materials. Further, it is well known that a transplanted artificial material different in mechanical characteristics from internal organs may cause a biological reaction according to the difference of the mechanical characteristics. Accordingly, a material having excellent mechanical characteristics like internal organs is needed. If the stimuli-responsive polymer is used to make an actuator, it should have a mechanical strength capable of sufficiently enduring drag applied to the actuator.
Accordingly, there are various new polymers improved in mechanical characteristics. For example, JP 2012-12606-A discloses temperature-responsive-gelating poly(ethylene glycol-block-(DL-lactic acid-random-glycolic acid)-block-ethylene glycol); (PEG-PLGA-PEG) triblock copolymer and (PLGA-PEG-PLGA) triblock copolymer. Further, JP 2009-29967-A discloses a branched block copolymer consisting of branched polyether and polyester.
However, even such a polymer material cannot make it possible that the stimuli-responsive function, mechanical characteristics and required characteristics such as biodegradability, biocompatibility and low toxicity are not achieved high dimensionally at the same time since introduced functional group to improve mechanical characteristics would relatively decrease the number of temperature-responsive groups.
Thus the application convenience and excellent mechanical characteristics have never been achieved with any stimuli-responsive material.
To achieve application convenience and high mechanical characteristics at the same time, it would be helpful provide for the improvement of mechanical characteristics of stimuli-responsive polymers. For example, workability and efficiency would be greatly improved if the strong coatability and convenience to carry and easily supply a material to an application site are achieved, when the material is used as general coating material such as paint, adhesive and sealant, or as medical coating material such as wound dressing material and anti-adhesive material. Specifically, it would be helpful if the material is supplied in a liquid state to firmly coat an application site by giving a stimulus. Particularly, conventional sheet-type anti-adhesive materials may have problems as to adhesiveness on complicated shapes, handling ability and supply characteristics to diseased parts in an endoscopic or laparoscopic surgery.
It would there be helpful to provide a stimuli-responsive material capable of achieving the application convenience and mechanical characteristics, as well as a medical material comprising the stimuli-responsive material.